Real-time and accurate data of the renal function are needed to develop new approaches for the prevention and treatment of acute renal failure (ARF). Current techniques have neither the accuracy nor the resolution time required. A highly innovative approach, was recently developed for the real-time and accurate measurement of glomerular filtration rate (GFR). The technique determines, minute-to-minute, the rate of disappearance from the extracellular space (ES) of a radiolabeled GFR agent as measured with an external radioactivity counting device. Although the approach showed excellent results, the use of radioactivity, limit its application. As an alternative, this project proposes the use a GFR agent labeled with a laser fluorescent dye (FGFR). The project involves the synthesis of the agent, the design and assembly of an instrument to measure the laser-induced tissue fluorescence (LITF) and the initial validation of the technique in rats. The synthesis of the agent will be performed by labeling with a laser fluorescent dye a well established GFR agent. A laser photodiode will be used in the instrument for the excitation beam. The LITF will be measured and recorded for further processing. At a constant excitation, LITF should be proportional to the tissue concentration of FGFR. This concept will be validated in rats by comparing the LITF with direct tissue concentration after extraction of the dye. This alternative method should represent a significant advance, not only for immediate detection of renal dysfunction to avert ARF, but also for the instant evaluation of the response to therapy in patients with ARF. PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE